Resonant Dynamical Friction at The Galactic Center

In this talk I will derive an analytical model for the so-called phenomenon of ‘resonant dynamical friction’, where a disc of stars around a super-massive black hole interacts with a massive perturber, so as to align its inclination with the disc’s orientation. I shall show that it stems from singular behaviour of the orbit-averaged equations of motion, which leads to a rapid alignment of the argument of the ascending node Ω of each of the disc stars, with that of the perturber, Ω_p, with a phase-difference of 90°. This phenomenon occurs for all stars whose maximum possible dΩ/dt (maximised over all values of Ω for all the disc stars), is greater than dΩ_p/dt; this corresponds approximately to all stars whose semi-major axes are less than twice that of the perturber. This persists until the perturber enters the disc. I will show that the predictions of this model agree with a suite of numerical N-body simulations which were perform to explore this phenomenon, for a wide range of initial conditions, masses, etc., and are an instance of a general phenomenon. Similar effects could occur in the context of planetary systems, too.